Periodontal disease represents a group of inflammatory diseases, which lead to the destruction of the gingiva and the supporting structures of the teeth. The loss of tissue results from an imbalance of the host immune response induced by the colonization of specific sub-gingival bacteria. This microflora is also considered the source for extra-oral diseases. Aggregatibacter actinomycetemcomitans is a Gram-negative periodontal pathogen associated with both the chronic and localized aggressive forms of the disease. Multiple disseminated extra-oral diseases are attributed to this pathogen including infective endocarditis and the potentiation of cardiovascular disease. However, the tropism used by A. actinomycetemcomitans to colonize the oral cavity or infiltrate and disseminate to distant tissues has remained elusive. These tissues share common extracellular matrix (ECM) proteins including collagen. Our group has identified a novel protein, extracellular matrix protein adhesin A (EmaA), which is critical for the interaction of the bacterium with collagens and is a proven virulence determinant for the initiation of infective endocarditis. In summary, A. actinomycetemcomitans expresses a cell surface adhesin that binds collagen, the most abundant ECM protein, for establishing infectious foci. Therefore, we posit that ECM colonization acts as a reservoir for re-infection of the gingival sulcus and dissemination to extra oral sites. The EmaA adhesin is composed of three identical monomers unique to A. actinomycetemcomitans that intercalate in the outer membrane to assemble unique antenna-like surface appendages essential for collagen binding. However, the protein size and sequence of the monomers is serotype specific. Furthermore, EmaA is posttranslationally modified with O-polysaccharide (O-PS) sugars that are crucial for binding to collagen. Interestingly, this EmaA modification shares the same enzymes required for O-PS biosynthesis. The specific role of the glycan moieties in the interaction with collagen remains undefined. The goal of this application is to elucidate the mechanism(s) utilized by this pathogen for colonizing the oral cavity and disseminating to other tissues. To achieve this goal we propose the following specific aims: 1) determine the localization and composition of the glycan moiety of EmaA from serotype b bacteria; 2) determine the role of EmaA genotype and bacterial serotype in collagen binding; and 3) biochemical and biophysical determination of the EmaA/collagen interaction. Defining the nature of the active binding moiety of EmaA will aid in understanding the role of this protein in the pathogenesis of A. actinomycetemcomitans. The new insights gained from this study into the molecular mechanism of this adhesin will lead to the development of molecules to disrupt and/or diminish tissue colonization by this pathogen.